Projector-type image display apparatus

ABSTRACT

At least one exemplary embodiment is directed to a projector which includes several optical elements, reflective devices and beam splitters, arranged to reduce back reflection effects. At least one exemplary embodiment includes a mirror, two beam splitters, three reflection devices, and two optical elements affecting polarization of incident light upon the optical elements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projector and more particularly,though not exclusively, to a projector that modulates a light beam via areflective liquid-crystal panel.

2. Description of the Related Art

Reflective liquid-crystal panels have a higher aperture ratio and higherdefinition than transmissive liquid-crystal panels, and therefore,projectors equipped with reflective liquid-crystal panels are in greatdemand. However, in contrast to transmissive-type projectors,reflective-type projectors have the two following optical problems,which have been setting back the popularization of reflective-typeprojectors.

One of the problems is that a reflection of image light produced in anoptical projecting system re-enters the reflective liquid-crystal panelwhere the light is reflected again so as to re-enter the opticalprojecting system. As a result, the light passes through the opticalprojecting system to reach the screen, causing the image contrast todecrease. The other problem is that the light needs to be selecteddepending on whether the reflective liquid-crystal panel is in an ONmode (a mode in which light is projected) or an OFF mode (a mode inwhich light is not projected), a polarizing beam splitter must bedisposed in front of the panel. For this reason, the colorseparating/combining system tends to become large in size.

As an attempt to solve the first problem, U.S. Pat. No. 5,268,775 andU.S. Pat. No. 5,786,873 disclose examples in which the direction ofpolarization of feedback light is rotated by about 90° (e.g., by using aquarter-waveplate) so that the feedback light is substantially removedby a polarizing beam splitter and a polarizer.

On the other hand, for the purpose of solving the second problem, USAA2002/0140905 discusses a system in which two polarizing beam splittersare provided with respect to three reflective liquid-crystal panelscorresponding to three primary colors, such that color separation andcolor combination are performed in the two polarizing beam splitters.According to US AA2002/0140905, wavelength-selective polarizationrotators are provided proximate an incident side and an exit side ofeach polarizing beam splitter. This facilitates the control of theON-OFF mode of two of the reflective liquid-crystal panels by one of thepolarizing beam splitters, so as to select whether to project or not toproject light.

However, simply combining these two examples does not solve the twoaforementioned problems.

SUMMARY OF THE INVENTION

At least one exemplary embodiment is directed to a projector-type imagedisplay apparatus. The projector-type image display apparatus includes afirst reflective liquid-crystal display panel corresponding to lightwithin a first wavelength range; a second reflective liquid-crystaldisplay panel corresponding to light within a second wavelength rangedifferent from the first wavelength range; an optical projecting systemconfigured to project the light received from the first reflectiveliquid-crystal display panel and the light received from the secondreflective liquid-crystal display panel; a first polarizing beamsplitter, where the first polarizing beam splitter guides light of afirst polarization direction included in the light of the firstwavelength range received from a light source towards the firstreflective liquid-crystal display panel, where the first polarizing beamsplitter guides light of a second polarization direction included in thelight reflected by the first reflective liquid-crystal display paneltowards the optical projecting system, the second polarization directionbeing substantially perpendicular to the first polarization direction,where the first polarizing beam splitter guides light of the secondpolarization direction included in the light of the second wavelengthrange received from the light source towards the second reflectiveliquid-crystal display panel, and where the first polarizing beamsplitter guides light of the first polarization direction included inthe light reflected by the second reflective liquid-crystal displaypanel towards the optical projecting system; a first polarizer disposedbetween the first polarizing beam splitter and the optical projectingsystem, the first polarizer absorbing one of the light of the firstpolarization direction and the light of the second polarizationdirection, and transmitting the other one of the light of the firstpolarization direction and the light of the second polarizationdirection; and a first quarter-waveplate disposed between the firstpolarizer and the optical projecting system.

At least one exemplary embodiment is directed to a projector-type imagedisplay apparatus, which includes a first reflective liquid-crystaldisplay panel corresponding to light within a first wavelength range; asecond reflective liquid-crystal display panel corresponding to lightwithin a second wavelength range different from the first wavelengthrange; an optical projecting system configured to project the lightreceived from the first reflective liquid-crystal display panel and thelight received from the second reflective liquid-crystal display panel;a first polarizing beam splitter, where the first polarizing beamsplitter guides light of a first polarization direction included in thelight of the first wavelength range received from a light source towardsthe first reflective liquid-crystal display panel, where the firstpolarizing beam splitter guides light of a second polarization directionincluded in the light reflected by the first reflective liquid-crystaldisplay panel towards the optical projecting system, the secondpolarization direction being substantially perpendicular to the firstpolarization direction, where the first polarizing beam splitter guideslight of the second polarization direction included in the light of thesecond wavelength range received from the light source towards thesecond reflective liquid-crystal display panel, and where the firstpolarizing beam splitter guides light of the first polarizationdirection included in the light reflected by the second reflectiveliquid-crystal display panel towards the optical projecting system; afirst polarizer disposed between the first polarizing beam splitter andthe optical projecting system, the first polarizer transmitting one ofthe light of the first polarization direction and the light of thesecond polarization direction, and guiding the other one of the light ofthe first polarization direction and the light of the secondpolarization direction towards the outside of an optical path extendingbetween the first polarizing beam splitter and the optical projectingsystem; and a first quarter-waveplate disposed between the firstpolarizer and the optical projecting system.

At least one exemplary embodiment is directed to a projector-type imagedisplay apparatus, which includes a plurality of reflectiveliquid-crystal display panels corresponding to light beams in differentwavelength ranges; an optical-path combining system configured tocombine optical paths of the light beams received from the plurality ofreflective liquid-crystal display panels; an optical projecting systemconfigured to project the light beams received from the optical-pathcombining system; and a retardation plate disposed between theoptical-path combining system and the optical projecting system. Theoptical-path combining system includes a plurality of polarizers.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a first exemplary embodiment.

FIG. 2 is a schematic diagram illustrating a modification example of thefirst exemplary embodiment.

FIG. 3 illustrates the characteristics of a color combiner according toat least one exemplary embodiment.

FIG. 4 is a schematic diagram illustrating a second exemplaryembodiment.

FIG. 5 is a schematic diagram illustrating a third exemplary embodiment.

FIG. 6 is a schematic diagram illustrating a fourth exemplaryembodiment.

DESCRIPTION OF THE EMBODIMENTS

The following description of exemplary embodiment(s) is merelyillustrative in nature and is in no way intended to limit the invention,its application, or uses

Processes, techniques, apparatus, and materials as known by one ofordinary skill in the relevant art may not be discussed in detail butare intended to be part of the enabling description where appropriate.

Additionally, the actual size of optical elements may not be discussedhowever any size from macro lenses to nano lenses are intended to liewithin the scope of exemplary embodiments (e.g., lenses with diametersof nanometer size, micro size, centimeter size, and meter sizes).

Notice that similar reference numerals and letters refer to similaritems in the following figures, and thus once an item is defined in onefigure, it may not be discussed for following figures.

Exemplary embodiments of an image display apparatus will now bedescribed with reference to the drawings.

First Exemplary Embodiment

FIG. 1 illustrates a color separating/combining system of an imagedisplay apparatus according to a first exemplary embodiment. The firstexemplary embodiment will be described below in detail with reference toFIG. 1. A white light beam released from a light source 1, which emitsunpolarized light, is reflected by a reflector and becomes asubstantially collimated light beam 2. The white light beam can be splitinto three primary colors, (e.g., red, green, and blue colors). Thesethree primary colors will respectively be defined as a red lightcomponent 2 r corresponding to a wavelength range of red color; a greenlight component 2 g corresponding to a wavelength range of green color;and a blue light component 2 b corresponding to a wavelength range ofblue color.

A polarization converter 3 is disposed in an intermediate section of anoptical illumination system and is defined by a polarization-convertingarray arranged substantially perpendicular to the optical axis. Thepolarization converter 3 aligns the direction of polarization of theselight components so as to facilitate p-polarization of these lightcomponents. Thus, these light components are in a polarized state inwhich the electric field vibrates in a direction substantially parallelto the drawing plane of FIG. 1. As a result, the red light component 2 rbecomes a p-polarized red light component 4 r, the green light component2 g becomes a p-polarized green light component 4 g, and the blue lightcomponent 2 b becomes a p-polarized blue light component 4 b. In thiscase, although all the color light components in the visible rangeincluded in the unpolarized light are p-polarized by the polarizationconverter 3, these color light components can alternatively bes-polarized. As a further alternative, the direction of polarization ofone of the color light components can be made substantiallyperpendicular to that of the two remaining color light components.Furthermore, the polarization converter 3 can be omitted if the lightsource 1 is a type that emits a light beam substantially in thedirection of polarization (e.g., a laser light source). In a case wherea laser light source is used, a polarizer can simply be provided.Moreover, in this case, the laser light source can be provided with aplurality of laser light-source components corresponding to the threecolors. The laser light-source components can be arranged in a mannersuch that the direction of polarization of a color light beam emittedfrom one of the laser light-source components is substantiallyperpendicular to the direction of polarization of the remaining colorlight beams emitted from the other light-source components correspondingto the remaining colors.

A dichroic mirror 5 is provided such that it selectively reflects greenlight components. This means that the dichroic mirror 5 reflects thep-polarized green light component 4 g while transmitting the p-polarizedred light component 4 r and the p-polarized blue light component 4 b. Onthe other hand, in a case where the dichroic mirror 5 is agreen-transmissive type, the properties of the dichroic mirror 5 arebasically opposite to the description above, and therefore, adescription of such a case will be omitted here. The p-polarized redlight component 4 r and the p-polarized blue light component 4 btransmitted through the dichroic mirror 5 pass through a polarizer 6where the degree of polarization of these light components 4 r and 4 bis increased. Subsequently, the light components 4 r and 4 b enter awavelength-selective polarization rotator 7.

The wavelength-selective polarization rotator 7 has the capability torotate the direction of polarization of red light components by about90° but not to rotate the direction of polarization of blue lightcomponents. The p-polarized red light component 4 r and the p-polarizedblue light component 4 b passing through the wavelength-selectivepolarization rotator 7 respectively become an s-polarized red lightcomponent 8 r and a p-polarized blue light component 8 b. Thes-polarized red light component 8 r and the p-polarized blue lightcomponent 8 b then enter a polarizing beam splitter 9.

The s-polarized red light component 8 r incident on the polarizing beamsplitter 9 is reflected by a polarization beam splitting surface 10 andthus enters a reflective liquid-crystal panel 11 r. The reflectiveliquid-crystal panel 11 r and reflective liquid-crystal panels 11 g and11 b facilitate the rotation by about 90° of the direction ofpolarization in an ON mode, but does not facilitate the rotation in anOFF mode. Here, the term “ON mode” refers to a display-ON mode in whichlight is guided towards a projection lens and is projected onto aprojection surface (e.g., a screen), whereas the term “OFF mode” refersto a display-OFF mode in which light is blocked from entering theprojection lens. Accordingly, in the ON mode, the s-polarized red lightcomponent 8 r becomes a p-polarized red light component 12 r whichre-enters the polarizing beam splitter 9. Due to being p-polarized thistime, the p-polarized red light component 12 r passes through thepolarization beam splitting surface 10 and thus exits the polarizingbeam splitter 9. On the other hand, although the s-polarized red lightcomponent 8 r is reflected by the polarization beam splitting surface 10in the OFF mode, the optical path of the light component 8 r reflectedfrom the reflective liquid-crystal panel 11 r in the OFF mode will beomitted in FIG. 1. Moreover, although a retardation plate (e.g., aquarter-waveplate) can be provided between the polarizing beam splitter9 and the reflective liquid-crystal panel 11 r to correct the directionof polarization of angled incident light components, such a retardationplate is also not shown in FIG. 1.

On the other hand, due to being p-polarized, the p-polarized blue lightcomponent 8 b passes through the polarization beam splitting surface 10and thus enters the reflective liquid-crystal panel 11 b. When thereflective liquid-crystal panel 11 b is in an ON mode, the p-polarizedblue light component 8 b becomes an s-polarized blue light component 12b which re-enters the polarizing beam splitter 9. Due to beings-polarized this time, the s-polarized blue light component 12 b isreflected by the polarization beam splitting surface 10 and thus exitsthe polarizing beam splitter 9.

On the other hand, the p-polarized green light component 4 g reflectedby the dichroic mirror 5 passes through a polarizer 13 where the degreeof polarization of the p-polarized green light component 4 g isincreased. The p-polarized green light component 4 g then enters apolarizing beam splitter 14 so as to reach a polarization beam splittingsurface 15. The p-polarized green light component 4 g passes through thepolarization beam splitting surface 15 and enters the reflectiveliquid-crystal panel 11 g. When the reflective liquid-crystal panel 11 gis in an ON mode, the p-polarized green light component 4 g becomes ans-polarized green light component 12 g which re-enters the polarizingbeam splitter 14. Due to being s-polarized this time, the s-polarizedgreen light component 12 g is reflected by the polarization beamsplitting surface 15 and thus exits the polarizing beam splitter 14.

In addition to the color light components 12 r, 12 g, 12 b that arepolarized ideally by about 90° by the respective reflectiveliquid-crystal panels 11 r, 11 g, 11 b in an ON mode, the light releasedfrom the corresponding polarizing beam splitters 9, 14 and directedtowards a color combiner (optical-path combiner) 19 actually containslight portions that lower the image contrast. Specifically, of the lightguided towards the light source 1 by the polarizing beam splitters 9, 14via pixels of the reflective liquid-crystal panels 11 r, 11 g, 11 b inan OFF mode, light portions leaking towards the projection lens 22 viathe polarizing beam splitters 9, 14 can be included in the lightreleased from the polarizing beam splitters 9, 14. Removal of theselight portions reduces the effect they have on lowering the imagecontrast.

Consequently, a polarizer 16A, which polarizes at least green and redlight components or green and blue light components, is disposedproximate the exit side of the polarizing beam splitter 14. Thus, thes-polarized green light component 12 g exiting the polarizing beamsplitter 14 becomes an s-polarized green light component 18 g havingbeen substantially removed from its undesirable polarized light portion.The s-polarized green light component 18 g then enters the colorcombiner 19. In this case, the polarizer 16A can absorb the undesirablepolarized light portion, or can reflect the undesirable polarized lightportion towards the outside of the optical path (i.e., verticallyup/down the page). According to at least one exemplary embodiment, sincethe absorbed light portion will not proceed along the optical path, theabsorption of the undesirable polarized light portion is included in themeaning of the phrase “guide the undesirable polarized light portiontowards the outside of the optical path”.

On the other hand, a wavelength-selective polarization rotator 17 isdisposed proximate the exit side of the polarizing beam splitter 9, suchthat the wavelength-selective polarization rotator 17 has the capabilityto rotate the direction of polarization of blue light components byabout 90° but not to rotate the direction of polarization of red lightcomponents. Furthermore, a polarizer 16B is disposed proximate the exitside of the wavelength-selective polarization rotator 17. According tothis structure, the p-polarized red light component 12 r and thes-polarized blue light component 12 b passing through thewavelength-selective polarization rotator 17 respectively become ap-polarized red light component 18 r and a p-polarized blue lightcomponent 18 b. Moreover, the p-polarized red light component 18 r andthe p-polarized blue light component 18 b enter the polarizer 16B whereundesirable polarized light portions are substantially removedtherefrom. Here, the undesirable polarized light portions ares-polarized light portions of the red light component 18 r and the bluelight component 18 b. Subsequently, the p-polarized red light component18 r and the p-polarized blue light component 18 b enter the colorcombiner 19.

A color-combining surface 20 of the color combiner 19 is defined by agreen-reflective dichroic film which includes a dielectric multilayerfilm, such that the color-combining surface 20 reflects the s-polarizedgreen light component 18 g but transmits the p-polarized red lightcomponent 18 r and the p-polarized blue light component 18 b. Thecolor-combining surface 20 combines the optical paths of the red lightcomponent and the blue light component and the optical path of the greenlight component. FIG. 3 schematically illustrates the reflective andtransmissive characteristics of the red, green, and blue lightcomponents. Generally, the reflective wavelength range of a dichroicfilm is wider for s-polarized light than p-polarized light, meaning thatthe transmissive wavelength range is wider for p-polarized light thans-polarized light. According to the first exemplary embodiment, sincethe green light component 18 g is s-polarized and the red lightcomponent 18 r and the blue light component 18 b are p-polarized, thebandwidths of the three colors overlap with one another as shown in FIG.3. This facilitates efficient utilization of the colors.

The three color light components 18 r, 18 g, 18 b combine by the colorcombiner 19 pass through a retardation plate (quarter-waveplate) 21 andare projected onto a screen (not shown) by a projection lens 22. Theprojection lens 22 can alternatively include, for example, a mirror.Although the first exemplary embodiment is being described based on afront projector, the first exemplary embodiment can alternatively bedirected to a rear projector. In that case, the projection lens 22 canproject an image onto a screen member that includes, for example, alenticular lens or a Fresnel lens.

The retardation plate 21 can have a phase difference of substantially aquarter-wavelength. When one of the color light components enters theprojection lens 22 via the retardation plate 21, a feedback lightportion of the color light component reflected by one of transmissiveplanes of the projection lens 22 returns to the retardation plate 21.The direction of polarization of the feedback light portion returning tothe retardation plate 21 is rotated by about 90° with respect to thedirection of polarization of the color light component that had enteredthe retardation plate 21 the first time. For example, a feedback lightportion of the s-polarized green light component 18 g reflected by theprojection lens 22 returns to the retardation plate 21, andsubsequently, the feedback light portion in a p-polarized state isreflected by the color combiner 19 and becomes incident on the polarizer16A where the feedback light portion is absorbed. In a similar fashion,feedback light portions of the p-polarized red light component 18 r andthe p-polarized blue light component 18 b are absorbed by the polarizer16B. In other words, each feedback light portion reflected by one of thetransmissive planes of the projection lens 22 is absorbed beforereaching the corresponding panel surface. Consequently, each feedbacklight portion reflected by the projection lens 22 and returning to thecorresponding retardation plate is absorbed by the correspondingpolarizer without returning to the projection lens 22 again. Thisreduces image deterioration (low contrast) on the screen, which iscaused by light reflection in the projection lens 22.

A modification of the first exemplary embodiment will be below describedwith reference to FIG. 2. In this example, the light components releasedfrom the polarization converter 3 a are s-polarized. Thus, these lightcomponents are in a polarized state in which the electric field vibratesin a direction substantially perpendicular to the drawing plane of FIG.2. This example is different from the first exemplary embodimentdescribed above in that the reflective liquid-crystal panel 11 g forgreen color is disposed in a different position along the optical pathof the green light component. Moreover, the green light component 12 gpassing through the polarizer 16A disposed proximate the exit side ofthe polarizing beam splitter 14 has its direction of polarizationrotated by about 90° by a half-retardation plate 23. Subsequently, thegreen light component 18 g, which is s-polarized by having its directionof polarization been rotated by about 90°, enters the color combiner 19.The s-polarized green light component 18 g is reflected by the colorcombiner 19 so as to enter the projection lens 22. In addition to thesedifferences, this example is also different from the first exemplaryembodiment described above in that the wavelength-selective polarizationrotator 7 a disposed in the optical paths of the red light component andthe blue light component has the capability to rotate the direction ofpolarization of the blue light component by about 90° but not to rotatethe direction of polarization of the red light component. The red lightcomponent 4 r and the blue light component 4 b passing through thewavelength-selective polarization rotator 7 a are respectively convertedto an s-polarized light component and a p-polarized light component.Other than these small structural differences, this modification examplebasically has the same structure as the first exemplary embodiment.

Alternatively, in the first exemplary embodiment, the dichroic mirror 5can be replaced with a polarizing beam splitter. In that case, in frontof the polarizing beam splitter, that is, between the polarizationconverter 3 and the polarizing beam splitter replaced with the dichroicmirror 5, a wavelength-selective polarization rotator(wavelength-selective retardation plate) can be provided. Thewavelength-selective polarization rotator (wavelength-selectiveretardation plate) can rotate the direction of polarization of a greenlight component by about 90° or can rotate the direction of polarizationof one of the two remaining color light components by about 90°.Alternatively, the wavelength-selective polarization rotator(wavelength-selective retardation plate) can rotate the direction ofpolarization of two of the color light components by about 90°. As afurther alternative, in addition to replacing the dichroic mirror 5 witha polarizing beam splitter, the laser light-source componentscorresponding to the three colors can be provided, as describedpreviously.

Furthermore, although the color combiner 19 is defined by a dichroicmirror or a dichroic prism in the first exemplary embodiment, the colorcombiner 19 can alternatively be a polarizing beam splitter. In thatcase, in view of the fact that the p-polarized feedback light portion ofthe green light component passes through the polarizing beam splitterdefining the color combiner 19, the polarizer 16B can absorb thep-polarized feedback light portion within the wavelength range of greencolor. On the other hand, due to the fact that the s-polarized feedbacklight portions of the blue and red light components are reflected by thepolarizing beam splitter defining the color combiner 19, the polarizer16A can absorb the s-polarized feedback light portions of the blue andred light components.

Second Exemplary Embodiment

FIG. 4 illustrates a second exemplary embodiment. Detailed descriptionsof some elements of the second exemplary embodiment are omitted due tothe fact that these elements are similar to those in the first exemplaryembodiment.

A white light beam emitted from the light source 1 is reflected by areflector and becomes a substantially collimated light beam 2. The whitelight beam can be split into three primary colors, for example, the redlight component 2 r, the green light component 2 g, and the blue lightcomponent 2 b.

The polarization converter 3 a disposed in the intermediate section ofthe optical illumination system aligns the direction of polarization ofthese light components so as to facilitate the s-polarization of theselight components. Thus, these light components are in a polarized statein which the electric field vibrates in a direction substantiallyperpendicular to the drawing plane of FIG. 4. As a result, the red lightcomponent 2 r becomes an s-polarized red light component 4 r, the greenlight component 2 g becomes an s-polarized green light component 4 g,and the blue light component 2 b becomes an s-polarized blue lightcomponent 4 b.

The dichroic mirror 5 selectively reflects green light components,meaning that the dichroic mirror 5 reflects the s-polarized green lightcomponent 4 g while transmitting the s-polarized red light component 4 rand the s-polarized blue light component 4 b. The s-polarized red lightcomponent 4 r and the s-polarized blue light component 4 b transmittedthrough the dichroic mirror 5 pass through the polarizer 6 such that thedegree of polarization of these light components 4 r and 4 b isincreased. Subsequently, the light components 4 r and 4 b enter thewavelength-selective polarization rotator 7 a.

The wavelength-selective polarization rotator 7 a has the capability torotate the direction of polarization of blue light components by about90° but not to rotate the direction of polarization of red lightcomponents. Thus, the s-polarized red light component 4 r and thes-polarized blue light component 4 b passing through thewavelength-selective polarization rotator 7 a respectively become ans-polarized red light component 8 r and a p-polarized blue lightcomponent 8 b. The s-polarized red light component 8 r and thep-polarized blue light component 8 b then enter the polarizing beamsplitter 9.

The s-polarized red light component 8 r incident on the polarizing beamsplitter 9 is reflected by the polarization beam splitting surface 10and thus enters the reflective liquid-crystal panel 11 r. When thereflective liquid-crystal panel 11 r is in an ON mode, the s-polarizedred light component 8 r becomes a p-polarized red light component 12 rwhich re-enters the polarizing beam splitter 9. Due to being p-polarizedthis time, the p-polarized red light component 12 r passes through thepolarization beam splitting surface 10 and thus exits the polarizingbeam splitter 9.

On the other hand, due to being p-polarized, the p-polarized blue lightcomponent 8 b passes through the polarization beam splitting surface 10and thus enters the reflective liquid-crystal panel 11 b. When thereflective liquid-crystal panel 11 b is in an ON mode, the p-polarizedblue light component 8 b becomes an s-polarized blue light component 12b which re-enters the polarizing beam splitter 9. Due to beings-polarized this time, the s-polarized blue light component 12 b isreflected by the polarization beam splitting surface 10 and thus exitsthe polarizing beam splitter 9.

On the other hand, the s-polarized green light component 4 g reflectedby the dichroic mirror 5 passes through the polarizer 13 where thedegree of polarization of the s-polarized green light component 4 g isincreased. The s-polarized green light component 4 g then enters thepolarizing beam splitter 14 so as to reach the polarization beamsplitting surface 15. The s-polarized green light component 4 g isreflected by the polarization beam splitting surface 15 and thus entersthe reflective liquid-crystal panel 11 g. When the reflectiveliquid-crystal panel 11 g is in an ON mode, the s-polarized green lightcomponent 4 g becomes a p-polarized green light component 18 g whichre-enters the polarizing beam splitter 14. Due to being p-polarized thistime, the p-polarized green light component 18 g passes through thepolarization beam splitting surface 15 and thus exits the polarizingbeam splitter 14.

The p-polarized red light component 12 r and the s-polarized blue lightcomponent 12 b exiting the polarizing beam splitter 9 enter thewavelength-selective polarization rotator 17. The wavelength-selectivepolarization rotator 17 has the capability to rotate the direction ofpolarization of blue light components by about 90° but not to rotate thedirection of polarization of red light components. Thus, the p-polarizedred light component 12 r and the s-polarized blue light component 12 bpassing through the wavelength-selective polarization rotator 17respectively become a p-polarized red light component 18 r and ap-polarized blue light component 18 b. The p-polarized red lightcomponent 18 r and the p-polarized blue light component 18 b then enterthe color combiner 19.

The color-combining surface 20 of the color combiner 19 is defined by agreen-reflective dichroic film. The color-combining surface 20 combinethe optical paths of the p-polarized red light component 18 r, thep-polarized green light component 18 g, and the p-polarized blue lightcomponent 18 b. The p-polarized red light component 18 r, thep-polarized green light component 18 g, and the p-polarized blue lightcomponent 18 b released from the color combiner 19 pass through apolarizer 16 where undesirable polarized light portions aresubstantially removed from the light components 18 r, 18 g, and 18 b. Inthis case, the undesirable polarized light portions are s-polarizedlight portions. Subsequently, the p-polarized red light component 18 r,the p-polarized green light component 18 g, and the p-polarized bluelight component 18 b pass through the retardation plate 21 and areprojected onto a projection surface (e.g., a screen), by the projectionlens 22.

The retardation plate 21 can have a phase difference of substantially aquarter-wavelength and releases the color light components toward theprojection lens 22 in a manner such that all the color light componentshave their polarization state converted to a circularly polarized state.When one of the color light components enters the projection lens 22 viathe retardation plate 21, a feedback light portion of the color lightcomponent reflected by one of transmissive planes of the projection lens22 returns to the retardation plate 21. The direction of polarization ofthe feedback light portion returning to the retardation plate 21 isrotated by about 90° with respect to the direction of polarization ofthe color light component that had entered the retardation plate 21 thefirst time. Accordingly, after passing through the retardation plate 21,the feedback light portions of the p-polarized red light component 18 r,the p-polarized green light component 18 g, and the p-polarized bluelight component 18 b are absorbed by the polarizer 16. In other words,each feedback light portion reflected by one of the transmissive planesof the projection lens 22 is absorbed before reaching the correspondingpanel surface, and thus reflection and re-projection onto the screen isreduced. This reduces deterioration (low contrast) of the projectedimage on the screen.

Even though the second exemplary embodiment can be different withrespect to the first exemplary embodiment, in view of the efficiency ofcolor combining due to the fact that the red, green, and blue lightcomponents are released in the same polarized state, the secondexemplary embodiment can use a lesser number of parts and can provide aproduct at a lower cost.

Third Exemplary Embodiment

FIG. 5 illustrates a third exemplary embodiment. Detailed descriptionsof some elements of the third exemplary embodiment are omitted due tothe fact that these elements are similar to those in the first exemplaryembodiment.

A white light beam emitted from the light source 1 is reflected by areflector and becomes a substantially collimated light beam 2. The whitelight beam can be split into three primary colors, namely, the red lightcomponent 2 r, the green light component 2 g, and the blue lightcomponent 2 b.

The polarization converter 3 a disposed in the intermediate section ofthe optical illumination system aligns the direction of polarization ofthese light components so as to facilitate the s-polarization of theselight components. Thus, these light components are in a polarized statein which the electric field vibrates in a direction substantiallyperpendicular to the drawing plane of FIG. 5. As a result, the red lightcomponent 2 r becomes an s-polarized red light component 4 r, the greenlight component 2 g becomes an s-polarized green light component 4 g,and the blue light component 2 b becomes an s-polarized blue lightcomponent 4 b.

The dichroic mirror 5 selectively reflects green light components,meaning that the dichroic mirror 5 reflects the s-polarized green lightcomponent 4 g while transmitting the s-polarized red light component 4 rand the s-polarized blue light component 4 b. The s-polarized red lightcomponent 4 r and the s-polarized blue light component 4 b transmittedthrough the dichroic mirror 5 pass through the polarizer 6 where thedegree of polarization of these light components 4 r and 4 b isincreased. Subsequently, the light components 4 r and 4 b enter thewavelength-selective polarization rotator 7 a.

The wavelength-selective polarization rotator 7 a has the capability torotate the direction of polarization of blue light components by about90° but not to rotate the direction of polarization of red lightcomponents. The s-polarized red light component 4 r and the s-polarizedblue light component 4 b passing through the wavelength-selectivepolarization rotator 7 a respectively become an s-polarized red lightcomponent 8 r and a p-polarized blue light component 8 b. Thes-polarized red light component 8 r and the p-polarized blue lightcomponent 8 b then enter the polarizing beam splitter 9.

The s-polarized red light component 8 r incident on the polarizing beamsplitter 9 is reflected by the polarization beam splitting surface 10and thus enters the reflective liquid-crystal panel 11 r. When thereflective liquid-crystal panel 11 r is in an ON mode, the s-polarizedred light component 8 r becomes a p-polarized red light component 12 rwhich re-enters the polarizing beam splitter 9. Due to being p-polarizedthis time, the p-polarized red light component 12 r passes through thepolarization beam splitting surface 10 and thus exits the polarizingbeam splitter 9.

On the other hand, due to being p-polarized, the p-polarized blue lightcomponent 8 b passes through the polarization beam splitting surface 10and thus enters the reflective liquid-crystal panel 11 b. When thereflective liquid-crystal panel 11 b is in an ON mode, the p-polarizedblue light component 8 b becomes an s-polarized blue light component 12b which re-enters the polarizing beam splitter 9. Due to beings-polarized this time, the s-polarized blue light component 12 b isreflected by the polarization beam splitting surface 10 and thus exitsthe polarizing beam splitter 9.

On the other hand, the s-polarized green light component 4 g reflectedby the dichroic mirror 5 passes through the polarizer 13 where thedegree of polarization of the s-polarized green light component 4 g isincreased. The s-polarized green light component 4 g then enters thepolarizing beam splitter 14 so as to reach the polarization beamsplitting surface 15. The s-polarized green light component 4 g isreflected by the polarization beam splitting surface 15 and thus entersthe reflective liquid-crystal panel 11 g. When the reflectiveliquid-crystal panel 11 g is in an ON mode, the s-polarized green lightcomponent 4 g becomes a p-polarized green light component 12 g whichre-enters the polarizing beam splitter 14. Due to being p-polarized thistime, the p-polarized green light component 12 g passes through thepolarization beam splitting surface 15 and thus exits the polarizingbeam splitter 14.

The p-polarized red light component 12 r and the s-polarized blue lightcomponent 12 b exiting the polarizing beam splitter 9 enters thewavelength-selective polarization rotator 17. The wavelength-selectivepolarization rotator 17 has the capability to rotate the direction ofpolarization of blue light components by about 90° but not to rotate thedirection of polarization of red light components. Thus, the p-polarizedred light component 12 r and the s-polarized blue light component 12 bpassing through the wavelength-selective polarization rotator 17respectively become a p-polarized red light component 18 r and ap-polarized blue light component 18 b. The p-polarized red lightcomponent 18 r and the p-polarized blue light component 18 b then passthrough the polarizer 16B where undesirable polarized light portions aresubstantially removed from the p-polarized red light component 18 r andthe p-polarized blue light component 18 b. Subsequently, the p-polarizedred light component 18 r and the p-polarized blue light component 18 bpass through a retardation plate 21B so as to enter the color combiner19.

On the other hand, the p-polarized green light component 12 g releasedfrom the polarizing beam splitter 14 is transmitted through thepolarizer 16A where an undesirable polarized light portion issubstantially removed from the p-polarized green light component 12 g.The p-polarized green light component 12 g thus becomes a p-polarizedgreen light component 18 g. In this case, the undesirable polarizedlight portion is an s-polarized light portion. Subsequently, thep-polarized green light component 18 g passes through a retardationplate 21A so as to enter the color combiner 19.

The retardation plates 21A, 21B give a phase difference of substantiallya quarter-wavelength to the corresponding color light components.Consequently, the p-polarized red light component 18 r, the p-polarizedgreen light component 18 g, and the p-polarized blue light component 18b enter the color combiner 19 in a circularly polarized state.

The color-combining surface 20 of the color combiner 19 is defined by agreen-reflective dichroic film, meaning that the color-combining surface20 transmits red and blue colors. The color-combining surface 20combines the optical paths of the p-polarized red light component 18 r,the p-polarized green light component 18 g, and the p-polarized bluelight component 18 b. The p-polarized red light component 18 r, thep-polarized green light component 18 g, and the p-polarized blue lightcomponent 18 b released from the color combiner 19 enter the projectionlens 22 in a state where their optical paths are combined, and aresubsequently projected onto a screen by the projection lens 22.

According to this structure, a green light component reflected by theprojection lens 22 re-enters the retardation plate 21A so as to becomeincident on the polarizer 16A in an s-polarized state. As a result, thisreflected green light component is absorbed by the polarizer 16A.Similarly, red and blue light components reflected by the projectionlens 22 re-enter the retardation plate 21B so as to become incident onthe polarizer 16B in an s-polarized state. As a result, these reflectedred and blue light components are absorbed by the polarizer 16B.Accordingly, since the polarizers 16A, 16B absorb light components thatcould cause contrast deterioration when these light components arereflected by the projection lens 22 and are reflected again to beprojected back onto the screen, the projected image deterioration due tolow contrast is reduced.

Although the third exemplary embodiment can use a larger number of partsin comparison with the first exemplary embodiment, the third exemplaryembodiment can reduce the number of surfaces through which the lightcomponents pass after the retardation plates. Accordingly, since thefeedback light portions caused by surface reflection can be furtherreduced, higher contrast can be achieved.

Fourth Exemplary Embodiment

FIG. 6 illustrates a color separating/combining system according to afourth exemplary embodiment. The fourth exemplary embodiment will bedescribed below in detail with reference to FIG. 6. The fourth exemplaryembodiment shown in FIG. 6 is common with the first exemplary embodimentshown in FIG. 1 in view of the following points. Specifically, one ofthe common points is the way the green light component of a light beamemitted from the light source 1 travels toward the color combiner(optical-path combining prism) 19. Another common point is how the redand blue light components of the light beam emitted from the lightsource 1 entering the polarization beam splitting surface 10 arerespectively reflected by the reflective liquid-crystal panels 11 r, 11b and re-enter the polarization beam splitting surface 10. Moreover, inthe polarization beam splitting surface 10, the red and blue lightcomponents have their optical paths of image light combined, andsubsequently exit the polarizing beam splitter 9 so as to travel towardsthe color combiner 19. Detailed descriptions of some elements of thefourth exemplary embodiment are omitted due to the fact that theseelements are similar to those in the first exemplary embodiment.

The fourth exemplary embodiment differs from the first exemplaryembodiment in that the s-polarized blue light component 12 b (in whichthe electromagnetic wave vibrates in a direction substantiallyperpendicular to the drawing plane of FIG. 6) released from thepolarizing beam splitter 9 and the p-polarized red light component 12 rreleased from the polarizing beam splitter 9 enter the color combiner 19respectively via a blue-designated polarizer 16C and a red-designatedpolarizer 16D. Specifically, the blue-designated polarizer 16C guides ans-polarized light portion included in a light component corresponding tothe blue wavelength range towards the projection lens 22 while blocking,or absorbing, a p-polarized light portion included in the blue lightcomponent from entering the projection lens 22. Moreover, theblue-designated polarizer 16C guides a light component corresponding tothe red wavelength range entirely towards the projection lens 22(although there may be cases where the transmittance is not 100%, thetransmittance or the reflectance of the blue-designated polarizer 16C isset at a selected percentage (e.g., about 90%, greater than or equal to95%) with respect to both s-polarized and p-polarized light portions).On the other hand, the red-designated polarizer 16D guides a p-polarizedlight portion included in a light component corresponding to the redwavelength range towards the projection lens 22 while blocking, orabsorbing, an s-polarized light included in the red light component fromentering the projection lens 22. Moreover, the red-designated polarizer16D guides a light component corresponding to the blue wavelength rangeentirely towards the projection lens 22. In this case, whichever one ofthe blue-designated polarizer 16C and the red-designated polarizer 16Dcan be disposed closer to the light source 1. Alternatively, theblue-designated polarizer 16C and the red-designated polarizer 16D canbe integrated with each other. As a further alternative, awavelength-selective polarizer having the characteristics of both theblue-designated polarizer 16C and the red-designated polarizer 16D canbe disposed between the polarizing beam splitter 9 and the colorcombiner 19.

The blue-designated polarizer 16C functions as a polarizer for bluelight components, and functions as an optical member that transmits boths-polarized and p-polarized light portions for light components in thewavelength ranges of other colors. Similarly, the red-designatedpolarizer 16D functions as a polarizer for red light components, andfunctions as an optical member that transmits both s-polarized andp-polarized light portions for light components in the wavelength rangesof other colors. In order to contribute to an overall size reduction ofthe apparatus, the blue-designated polarizer 16C can transmit as-polarized light portion of the blue light component and absorb ap-polarized light portion of the blue light component, and can bedisposed substantially perpendicular to the optical axis. On the otherhand, the red-designated polarizer 16D can transmit a p-polarized lightportion of the red light component and absorb an s-polarized lightportion of the red light component, and can be disposed substantiallyperpendicular to the optical axis. The optical axis is defined by anoptical path of a main beam of light released from the center of eachreflective liquid-crystal panel or an optical path of the main beamextending back towards the light source 1. The p-polarized light portionof the blue light component can alternatively be reflected by theblue-designated polarizer 16C, but in that case, the blue-designatedpolarizer 16C can be disposed at an angle with respect to the opticalaxis. Therefore, this could lead to an increase in the size of theapparatus. Although the retardation plate 21 is disposed between thecolor combiner 19 and the projection lens 22 in the fourth exemplaryembodiment, the fourth exemplary embodiment is not limited to thisconfiguration. For example, due to the fact that the color combiner 19is defined by a dichroic prism or a dichroic mirror, a firstquarter-waveplate can be disposed between the polarizer 16A and thecolor combiner 19, and a second quarter-waveplate can be disposedbetween the red-designated polarizer 16D and the color combiner 19.

According to the structure described above, reflected light from theprojection lens 22 returning to the projection lens 22 is reduced,whereby contrast deterioration can be reduced. Accordingly, thisimproves the performance of the image display apparatus especially inview of the contrast properties.

The first, second, third, and fourth exemplary embodiments or portionsthereof can be combined with each other. Moreover, the red, green, andblue light components can be switched with one another in the aboveembodiments. Furthermore, in the above embodiments, instead of dividingthe visible range into red, green, and blue wavelength ranges, thevisible range can alternatively be divided into at least four wavelengthranges such that the apparatus corresponds to each light component ofthe corresponding wavelength range.

Furthermore, although at least a few exemplary embodiments are directedto a liquid-crystal display apparatus (e.g., having a plurality ofreflective liquid-crystal display panels and a plurality of polarizingbeam splitters) configured to perform color separation and colorcombination, at least one exemplary embodiment can alternatively beapplied to transmissive liquid crystal projectors and single-panelliquid-crystal projectors. In a case where an exemplary embodiment isdirected to a transmissive liquid-crystal projector, the optical pathextending from each reflective liquid-crystal panel to the opticalprojecting system defined by the projection lens 22 according to theabove embodiments can be applied similarly to the transmissiveliquid-crystal projector, and the optical illumination system disposedupstream of the optical path can be combined with a typical opticalsystem.

A projector-type image display apparatus equipped with reflectiveliquid-crystal panels, in accordance with at least one exemplaryembodiment, facilitates the reduction of the two aforementionedproblems, further facilitating the achievement of a higher contrast.Furthermore, a color separating/combining system, in accordance with atleast one exemplary embodiment, facilitates a simple-structured,low-cost projector equipped with reflective liquid-crystal panels andhaving high contrast properties.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

This application claims the benefit of Japanese Application No.2004-269956 filed Sep. 16, 2004, which is hereby incorporated byreference herein in its entirety.

1. A projector-type image display apparatus comprising: a firstreflective liquid-crystal display panel configured to receive andreflect light within a first wavelength range; a second reflectiveliquid-crystal display panel configured to receive and reflect lightwithin a second wavelength range different from the first wavelengthrange; projection optical system configured to project the lightreflected from the first reflective liquid-crystal display panel and thelight reflected from the second reflective liquid-crystal display panel;a first polarizing beam splitter, wherein the first polarizing beamsplitter guides light of a first polarization direction included in thelight of the first wavelength range received from a light source towardsthe first reflective liquid-crystal display panel, wherein the firstpolarizing beam splitter guides light of a second polarization directionincluded in the light reflected by the first reflective liquid-crystaldisplay panel towards the projection optical system, the secondpolarization direction being perpendicular to the first polarizationdirection, wherein the first polarizing beam splitter guides light ofthe second polarization direction included in the light of the secondwavelength range received from the light source towards the secondreflective liquid-crystal display panel, and wherein the firstpolarizing beam splitter guides light of the first polarizationdirection included in the light reflected by the second reflectiveliquid-crystal display panel towards the projection optical system; afirst polarizer disposed between the first polarizing beam splitter andthe projection optical system, the first polarizer absorbing one of thelight of the first polarization direction and the light of the secondpolarization direction, and transmitting the other one of the light ofthe first polarization direction and the light of the secondpolarization direction; a first quarter-waveplate disposed between thefirst polarizer and the projection optical system; a third reflectiveliquid-crystal display panel configured to receive and reflect lightwithin a third wavelength range different from the first and secondwavelength ranges; a second polarizing beam splitter which guides lightof the first polarization direction included in the light of the thirdwavelength range received from the light source towards the thirdreflective liquid-crystal display panel, and guides light of the secondpolarization direction included in the light reflected by the thirdreflective liquid-crystal display panel towards the projection opticalsystem; and an optical-path combiner which combines an optical path ofthe light released from the first polarizing beam splitter and anoptical path of the light released from the second polarizing beamsplitter, and guides the combined optical path towards the projectionoptical system, wherein the light in the first wavelength range, thelight in the second wavelength range, and the light in the thirdwavelength range enter the projection optical system in a manner suchthat the direction of polarization of the light in one of the wavelengthranges is different from the direction of polarization of the light inthe two remaining wavelength ranges.
 2. The projector-type image displayapparatus according to claim 1, further comprising awavelength-selective retardation plate disposed between the firstpolarizing beam splitter and the first polarizer, thewavelength-selective retardation plate rotating the direction ofpolarization of the light in the first wavelength range by about 90° andnot changing the direction of polarization of the light in the secondwavelength range.
 3. The projector-type image display apparatusaccording to claim 1, wherein the optical-path combiner includes adichroic film which reflects at least one of the light in the firstwavelength range, the light in the second wavelength range, and thelight in the third wavelength range, and transmits the light in theremaining wavelength ranges.
 4. The projector-type image displayapparatus according to claim 1, wherein the optical-path combinerdefines a third polarizing beam splitter which selectively guides thelight in the first wavelength range, the light in the second wavelengthrange, and the light in the third wavelength range towards theprojection optical system based on the direction of polarization.
 5. Theprojector-type image display apparatus according to claim 1, furthercomprising a second polarizer disposed between the second polarizingbeam splitter and the optical-path combiner, the second polarizerabsorbing the light of the first polarization direction, wherein thefirst polarizer is disposed between the first polarizing beam splitterand the optical-path combiner, and wherein the first quarter-waveplateis disposed between the optical-path combiner and the projection opticalsystem.
 6. The projector-type image display apparatus according to claim1, further comprising a second polarizer and a second quarter-waveplatewhich are disposed between the second polarizing beam splitter and theoptical-path combiner in that order from the second polarizing beamsplitter, wherein the first polarizer and the first quarter-waveplateare disposed between the first polarizing beam splitter and theoptical-path combiner in that order from the first polarizing beamsplitter.
 7. The projector-type image display apparatus according toclaim 1, wherein the first polarizer blocks the light of the firstpolarization direction included in the light of the first wavelengthrange from entering the projection optical system, and guides the lightof the second polarization direction included in the light of the firstwavelength range towards the projection optical system, and wherein thefirst polarizer guides the light of the first polarization direction andthe light of the second polarization direction included in the light ofthe second wavelength range towards the projection optical system. 8.The projector-type image display apparatus according to claim 1, furthercomprising a second polarizer disposed between the first polarizing beamsplitter and the projection optical system, wherein the second polarizerblocks the light of the second polarization direction included in thelight of the second wavelength range from entering the projectionoptical system, and guides the light of the first polarization directionincluded in the light of the second wavelength range towards theprojection optical system, and wherein second polarizer guides the lightof the first polarization direction and the light of the secondpolarization direction included in the light of the first wavelengthrange towards the projection optical system.
 9. The projector-type imagedisplay apparatus according to claim 1, wherein the first polarizerblocks the light of the first polarization direction included in thelight of the first wavelength range from entering the projection opticalsystem, and guides the light of the second polarization directionincluded in the light of the first wavelength range towards theprojection optical system, and wherein the first polarizer blocks thelight of the second polarization direction included in the light of thesecond wavelength range from entering the projection optical system, andguides the light of the first polarization direction included in thelight of the second wavelength range towards the projection opticalsystem.
 10. A projector-type image display apparatus comprising: a firstreflective liquid-crystal display panel configured to receive andreflect light within a first wavelength range; a second reflectiveliquid-crystal display panel configured to receive and reflect lightwithin a second wavelength range different from the first wavelengthrange; a projection optical system configured to project the lightreflected from the first reflective liquid-crystal display panel and thelight reflected from the second reflective liquid-crystal display panel;a first polarizing beam splitter, wherein the first polarizing beamsplitter guides light of a first polarization direction included in thelight of the first wavelength range received from a light source towardsthe first reflective liquid-crystal display panel, wherein the firstpolarizing beam splitter guides light of a second polarization directionincluded in the light reflected by the first reflective liquid-crystaldisplay panel towards the projection optical system, the secondpolarization direction being perpendicular to the first polarizationdirection, wherein the first polarizing beam splitter guides light ofthe second polarization direction included in the light of the secondwavelength range received from the light source towards the secondreflective liquid-crystal display panel, and wherein the firstpolarizing beam splitter guides light of the first polarizationdirection included in the light reflected by the second reflectiveliquid-crystal display panel towards the projection optical system; afirst polarizer disposed between the first polarizing beam splitter andthe projection optical system, the first polarizer absorbing one of thelight of the first polarization direction and the light of the secondpolarization direction, and transmitting the other one of the light ofthe first polarization direction and the light of the secondpolarization direction; a first quarter-waveplate disposed between thefirst polarizer and the projection optical system; a third reflectiveliquid-crystal display panel configured to receive and reflect lightwithin a third wavelength range different from the first and secondwavelength ranges; a second polarizing beam splitter which guides lightof the first polarization direction included in the light of the thirdwavelength range received from the light source towards the thirdreflective liquid-crystal display panel, and guides light of the secondpolarization direction included in the light reflected by the thirdreflective liquid-crystal display panel towards the projection opticalsystem; and an optical-path combiner which combines an optical path ofthe light released from the first polarizing beam splitter and anoptical path of the light released from the second polarizing beamsplitter, and guides the combined optical path towards the projectionoptical system, wherein the first polarizer is disposed between theoptical-path combiner and the projection optical system.
 11. Aprojector-type image display apparatus comprising: a first reflectiveliquid-crystal display panel configured to receive and reflect lightwithin a first wavelength range; a second reflective liquid-crystaldisplay panel configured to receive and reflect light within a secondwavelength range different from the first wavelength range; anprojection optical system configured to project the light reflected fromthe first reflective liquid-crystal display panel and the lightreflected from the second reflective liquid-crystal display panel; afirst polarizing beam splitter, wherein the first polarizing beamsplitter guides light of a first polarization direction included in thelight of the first wavelength range received from a light source towardsthe first reflective liquid-crystal display panel, wherein the firstpolarizing beam splitter guides light of a second polarization directionincluded in the light reflected by the first reflective liquid-crystaldisplay panel towards the projection optical system, the secondpolarization direction being perpendicular to the first polarizationdirection, wherein the first polarizing beam splitter guides light ofthe second polarization direction included in the light of the secondwavelength range received from the light source towards the secondreflective liquid-crystal display panel, and wherein the firstpolarizing beam splitter guides light of the first polarizationdirection included in the light reflected by the second reflectiveliquid-crystal display panel towards the projection optical system; afirst polarizer disposed between the first polarizing beam splitter andthe projection optical system, the first polarizer absorbing one of thelight of the first polarization direction and the light of the secondpolarization direction, and transmitting the other one of the light ofthe first polarization direction and the light of the secondpolarization direction; a first quarter-waveplate disposed between thefirst polarizer and the projection optical system; a third reflectiveliquid-crystal display panel configured to receive and reflect lightwithin a third wavelength range different from the first and secondwavelength ranges; a second polarizing beam splitter which guides lightof the first polarization direction included in the light of the thirdwavelength range received from the light source towards the thirdreflective liquid-crystal display panel, and guides light of the secondpolarization direction included in the light reflected by the thirdreflective liquid-crystal display panel towards the projection opticalsystem; and an optical-path combiner which combines an optical path ofthe light released from the first polarizing beam splitter and anoptical path of the light released from the second polarizing beamsplitter, and guides the combined optical path towards the projectionoptical system, wherein the light in the first wavelength range, thelight in the second wavelength range, and the light in the thirdwavelength range enter the quarter-waveplate in a manner such that thedirection of polarization of the light in one of the wavelength rangesis different from the direction of polarization of the light in the tworemaining wavelength ranges.
 12. A projector-type image displayapparatus comprising: a first reflective liquid-crystal display panelconfigured to receive and reflect light within a first wavelength range;a second reflective liquid-crystal display panel configured to receiveand reflect light within a second wavelength range different from thefirst wavelength range; an projection optical system configured toproject the light reflected from the first reflective liquid-crystaldisplay panel and the light reflected from the second reflectiveliquid-crystal display panel; a first polarizing beam splitter, whereinthe first polarizing beam splitter guides light of a first polarizationdirection included in the light of the first wavelength range receivedfrom a light source towards the first reflective liquid-crystal displaypanel, wherein the first polarizing beam splitter guides light of asecond polarization direction included in the light reflected by thefirst reflective liquid-crystal display panel towards the projectionoptical system, the second polarization direction being perpendicular tothe first polarization direction, wherein the first polarizing beamsplitter guides light of the second polarization direction included inthe light of the second wavelength range received from the light sourcetowards the second reflective liquid-crystal display panel, and whereinthe first polarizing beam splitter guides light of the firstpolarization direction included in the light reflected by the secondreflective liquid-crystal display panel towards the projection opticalsystem; a first polarizer disposed between the first polarizing beamsplitter and the projection optical system, the first polarizerabsorbing one of the light of the first polarization direction and thelight of the second polarization direction, and transmitting the otherone of the light of the first polarization direction and the light ofthe second polarization direction; a first quarter-waveplate disposedbetween the first polarizer and the projection optical system; whereinthe light in the first wavelength range and the light in the secondwavelength range enter the quarter-waveplate in a manner such that thedirection of polarization of the light in one of the wavelength rangesis different from the direction of polarization of the light in theother wavelength ranges.